1. Field of the Invention
The invention relates to the sciences of optics and human color perception in general and to the field of sunglass lenses in particular. More specifically, the invention relates to the application of optical polarization, trichroic spectral-filter technology, and the principles of human color perception, to produce sunglass lenses of unprecedented vision-enhancing capability.
2. Description of Related Technology
The principal benefit of wearing sunglasses is obvious. They provide comfort and protection for the eyes by attenuating excessively bright light. Virtually all modern sunglasses further protect the eyes by filtering out harmful but invisible ultraviolet light. Some of these also provide increased eye comfort by blocking infrared light, which can aggravate "dry-eye" and cause ocular discomfort--particularly among contact-lens wearers. Neutral-gray remains the most popular tint, with 10 to 20 percent luminous transmission being most common.
Some sunglasses operate on the principle of aggressively blocking certain portions of the visible spectrum: an example of these are the blue-blocking amber types. These feature high transmission of yellow, orange, and red, diminished transmission of green and blue-green, and virtually no transmission of blue and violet. Color values are highly distorted by lenses of this type, and despite acceptance of amber to enhance contrast, loss of chromatic contrast results as their deep yellow-orange tint weakens color differentiation.
Prior art amber lenses are often claimed to increase visual acuity by limiting transmission to the red half of the spectrum, thus reducing chromatic aberration inherent in human vision. By blocking short visible wavelengths--roughly those below 500 nm--which scatter readily in the atmosphere and are more difficult for the human eye to focus, the deeper shades of amber tints are said to increase the visibility of distant objects or those obscured by fog or haze. The prior art advocates blocking blue spectra (380-500 nm) while promoting yellow spectra (570-600 nm) to maximize visual acuity, especially in hazy or foggy conditions.
Polarized glasses reduce glare by blocking light which has become polarized by being reflected off various surfaces. This is accomplished by means well known to the art. Polarized light reflected off horizontal surfaces--and to a lesser degree, diagonal surfaces--can be blocked by polarized sunglasses. This improves visibility of the surface itself, and in the case of water and other transparent media, increased visibility beneath the surface. By removing blinding reflected glare, and the need to squint when facing it, polarized lenses also provide increased eye safety and comfort for the wearer.
In the past, the benefits of polarization as applied to sunglasses have been well known and exploited. Indeed there are many existing commercial examples of polarized sunglasses. These have been available in both plastic and glass lens constructions for decades. And while the neutral-tint polarized sunglasses of prior art can remove reflected glare quite effectively--thereby revealing previously-hidden color--they produce no further enhancements to color saturation or contrast beyond this "unveiling" effect.
Various colored polarized sunglass lenses are also available; these suffer from the same shortcomings and compromises found in all colored sunglass lenses of prior art--they all favor some colors at the expense of others. Sunglass lenses of prior art, polarized or not, which were intended to enhance vision by means of non-neutral (i.e., colored) tint exhibit intrinsic chromatic inaccuracy. Amber lenses weaken blue, rose lenses weaken green, green lenses weaken red, and so on. Ordinary gray lenses often weaken colors and contrast.
Each tint has particular advantages in particular circumstances but none has all. Tint selection has been determined in the past by user preference, and with regard to particular landscapes, seasons, and subjects viewed. The prior art has failed to combine into a single pair of sunglasses all the desirable characteristics and none of the unwanted compromises of the many known lens types and tints. In the sunglass industry a long-standing and unfulfilled need has existed for a lens which simultaneously provides: a) excellent glare reduction, b) enhanced color saturation, chromatic contrast, luminous contrast, and acuity, c) apparently neutral tint; d) high color fidelity; e) improved visibility or colored objects partially obscured by fog or haze; and f) complete UV protection. It would be desirable to provide all of these qualities simultaneously and, highly preferably, without compromise.